Mana before life

A defensive stat lets your mana soak damage: "% of damage taken from mana before life".

How it works. After block, evasion, armour, resistances and energy shield have done their work, the stat sends that percentage of the remaining damage to your current mana, one mana for one damage. If you run out of mana, the rest goes to life. The usual limit on the stat is 40%.

Costs and rules

Mana lost this way is simply gone, so there is less to cast with.
Mana reserved by passive spells is never touched (Spell types: active, passive, triggered).
Poison ticks skip energy shield but do take the mana share.
Mana regeneration, leech, mana on hit and the mana flask refill it normally, so they become defensive too. An automatic mana flask rule fires when damage drains your mana (Automatic flask rules).
You see "You lose N mana" in blue.

Sources. Item suffixes, a few notables in the sorcerer and druid sectors of the passive tree, and certain uniques (Affixes, The passive tree, Unique items).

Mind over Matter keystone. Sends 100% of the damage that gets past energy shield to mana. In return, you have no energy shield at all, and each point of damage costs 2 mana. Blood Magic and Wardbound Oath exclude it (Keystones).

Who benefits. Sorcerers, druids and mana-heavy paladins. A big mana pool, strong regeneration and leech make it work.

Dangers. You cannot cast with no mana, and a mana drain lowers your defence too. The Draining monster modifier removes mana (Monster modifiers).

The status bar displays the "Damage taken from mana" percentage in your stats window.